An approach has been developed for the rapid synthesis and screening of large numbers of small peptides with the aim of producing a molecule which mimics the high binding affinity and specificity of the larger natural ligands for enzymes and cellular receptors. Molecules with these attributes have been termed "mimetics" which have potential for many uses. For example, mimetics are attractive as therapeutic agents because they represent easily synthesized molecules. The current process represents an alternate strategy to the systematic alteration of natural ligands, which has proven slow and difficult, and the low probability approach of randomly screening compounds which do not have any known structural similarity to the natural ligand. The process makes possible the rapid simultaneous production of peptides in numbers larger than has been previously achieved by conventional solid phase synthetic methods and provides a way to readily determine and synthesize in pure form the specific sequences which are responsible for a desired activity.
The current process provides for several important advances over the prior art. Several reports using comparable solid-phase techniques show synthesis to be practically limited to several hundred peptides made at a time while the current process provides for the synthesis of peptides in virtually unlimited number.
Other recent reports, which accomplish production of very high numbers of small peptides in a short period of time using solid-phase technology, disclose the coupling of mixtures of amino acids to growing peptide chains. That approach requires regulation of the concentration of the amino acids in the mixtures to account for differing relative coupling rates of the amino acids in order that the concentrations of the resulting peptides are equal. In addition, that approach requires the application of multiple analytical techniques in order to determine the precise sequence which is responsible for the desired activity. The current process differs in that a single amino acid or group of amino acids is coupled at each coupling step obviating the need to account for differing coupling rates of the amino acids and ensuring the production of peptides in equimolar amounts. The current process also allows identification of the desired sequence and subsequent production in pure form without chemical analysis.
Still other reports teach inserting randomly synthesized oligonucleotides into filamentous phage. This biosynthetic method potentially allows the production of millions of small peptides, which, however, must be limited to genetically encoded amino acids and which can only have a linear configuration. The current invention allows for the inclusion of D-amino acids or otherwise modified amino acids and the synthesis of branched chain sequences, neither of which is possible with recombinant DNA methods.
Perhaps most importantly, in contrast to teachings in the prior art, the current process allows for evaluation of the peptides' ability to interact with the target binding site without the potential interference of the support resin. In short, this invention enables the production of a very large number of small peptides and provides the ability to readily identify the specific peptide or peptides which demonstrate a desired activity and to produce them in pure form.